I do not recommend Shorting the PSU like that, If you want to test it get a proper testing kit and a cheap voltmeter.
I would not have thought that the problem is the PSU at this stage. Take the Mobo out of the case to eliminate any possible shorts with the chassis, double/triple check that the CPU heatsink is installed correctly, It must be in full contact with the CPU otherwise the mobo will shutdown instantly to prevent frying the CPU. Take out the RAM, and make sure you have all power connectors in the motherboard, there may be as many as 3 or 4 different connectors including the 20-24 pin main atx connector.
Check that your jumpers are set to the default positions as per the manual.
Read and follow any power troubleshooting guide in your mobo manual.
I would not have thought that the problem is the PSU at this stage. Take the Mobo out of the case to eliminate any possible shorts with the chassis, double/triple check that the CPU heatsink is installed correctly, It must be in full contact with the CPU otherwise the mobo will shutdown instantly to prevent frying the CPU. Take out the RAM, and make sure you have all power connectors in the motherboard, there may be as many as 3 or 4 different connectors including the 20-24 pin main atx connector.
Check that your jumpers are set to the default positions as per the manual.
Read and follow any power troubleshooting guide in your mobo manual.